Interactive catalogue for pathogen elimination capacity
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Quantitative Microbial Risk Assessment is a preventive strategy for microbial safety of drinking water prepared from surface water (see picture below) and implemented in Dutch Legislation. The major components is determining the source water quality and the presence of microbial pathogens, assessment of the Pathogen Elimination Capacity of the treatment and exposure assessment and risk calculations.
Quantitative microbial risk assessment versus fecal indicator monitoring
Water can contain microbial, chemical and radiological contaminants that can cause adverse health effects when consumed. Providing water that is safe for drinking and other intended uses is crucial to prevent diseases in the community. Chemical contaminants typically don’t occur at levels that cause acute health effects, but long term exposure can lead to health problems. Microbial contamination however can cause acute outbreaks of disease, even at very low levels of contamination. Infected persons and animals shed high numbers of pathogenic microorganisms in their feces. These can be viruses, bacteria, protozoa or helminths. Helminths are mostly an issue in hot climates and very poor water treatment, but the other three pathogens are also relevant for developed countries as they are generally found in domestic waste water. Key characteristics of relevant waterborne pathogens in the Netherlands are summarized in Table 1.
Wastewater treatment has little effect on these pathogens, and therefore these pathogens are also found in surface waters affected by treated wastewater discharge. Livestock, wildlife, waterfowl and pets also contribute to contamination of surface water or other water sources. Ingestion of one or a few of these pathogens can already cause an infection, often leading to diarrhea and sometimes to more serious diseases (WHO 2011). Therefore microbial risks are the primary concern for safe water supply. The WHO (world health organization) promotes a risk based approach for drinking water supply, because water quality analysis only provides limited verification of drinking water safety (WHO 2011).
Microbial contamination with pathogenic viruses, bacteria or protozoa is relevant even below detection limits. Furthermore their occurrence can be highly variable, especially in small scale systems. Microbial water quality is tested for the absence of E. coli, an indicator bacteria present in high numbers in feces of warm blooded animals. Detection of E. coli is a clear indication of recent fecal contamination, however outbreaks of disease have occurred when E. coli was not detected. Therefore a routine water quality analysis doesn’t guarantee continuous safety. Besides routine monitoring, water companies in the Netherlands have the legal requirement to perform quantitative microbial risk assessment (QMRA) every three years (VROM 2005, Bichai and Smeets 2013).
The QMRA approach as applied to existing water supplies by the Dutch water companies is explained in the Manual.
*Bichai, F., & Smeets, P. W. M. H. (2013). Using QMRA-based regulation as a water quality management tool in the water security challenge: Experience from the Netherlands and Australia. Water Res, 47(20), 7315-7326. doi: http://dx.doi.org/10.1016/j.watres.2013.09.062
** VROM-Inspectorate. (2005). Inspectorate guideline; Assessment of the microbial safety of drinking water. the Netherlands.
The tool brings together top-quality and current knowledge on the removal of pathogenic micro-organisms in water treatment processes for use in risk assessment (QMRA). It interactively calculates the elimination capacity of the processes, and makes clear which process factors affect this capacity.
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